1. Field of the Invention
The present invention relates to a Ti-based brazing filler material, which is mainly used for brazing and soldering Ti or Ti-based alloy, and method for producing the Ti-based brazing filler material.
2. Description of Related Art
Titanium has features such as high specific strength (i.e., strength with regard to specific weight), high corrosion resistance, and high biocompatibility, and Ti alloys such as Ti-6Al-4V alloy have been used for various aerospace instruments, medical instruments, and the like. Ag-based or Al-based brazing filler materials have been conventionally and widely used for brazing such Ti alloys. Ag-based or AI-based brazing filler materials, however, have problems of resulting in low joint strength or insufficient corrosion resistance.
To these problems, Ti-based brazing filler materials have been developed. In particular, for the purpose of lowering the melting point, addition of Zr, Cu, Ni, and the like has been developed and put to practical use. These Ti-based brazing materials have a joint strength comparable to the base material as well as good corrosion resistance. For example, as disclosed in Japanese Patent Laid-Open Publication No. S59-220299 (Patent Literature 1), there was proposed an alloy in which Ni, Cu and Ag are added into Ti—Zr-based alloy. In addition, as disclosed in Japanese Patent Laid-Open Publication No. S59-126739 (Patent Literature 2), there was proposed an alloy in which various elements are added into an alloy comprising Ti, Zr, Hf and Cu.
The above-mentioned brazing filler materials comprising these alloys can be used for brazing Ti or Ti alloy or ceramics and the like, but are difficult to produce in ribbon form due to poor workability. It was therefore proposed that a brazing filler material be produced by liquid melt-spun ribbon production method, in which a molten alloy is ejected to the surface of cooling rolls which are rotating at a high speed.
On the other hand, some base materials to be brazed have complicated shapes and, in terms of latitude of the shape of the brazing filler material, it is also demanded, other than a ribbon, to produce a paste by mixing a powder and a binder. In this respect, melt-spun ribbons as disclosed in above-mentioned Patent Literatures 1 and 2 are difficult to meet this demand, and thus it is essential that a brazing filler material is powdered. Brazing filler materials in powder form are mainly categorized into two types as shown below.
One of the types is obtained by a mixing method, in which pure metal powders of individual elements, which constitutes an alloy to be a brazing filler material, are mixed in given proportions. The other type is obtained by producing an alloy to be a brazing filler material through atomizing method and the like, in which the brazing filler material consists of an alloy powder having a single composition. These two methods are applicable to conventional alloys such as Ni-based or Cu-based brazing filler materials, but are difficult to apply to Ti-based brazing filler materials as having a problem peculiar to Ti-base.
The problems peculiar to Ti-base are such that, in the mixing method, (1) an active metal powder such as Ti or Zr is oxidized; (2) it is difficult for alloying to proceed when jointing; and that, in atomizing method, (3) contamination occurs from the crucible when melting. For the problem of the above (1), for example, the section of background art of Patent Literature 2 describes that “active metal powder such as Ti and Zr tends to be easily oxidized to form an oxide on the surface of the powder, and this oxide remains in the joint part to become a factor for lowering credibility after jointing.”
For the above problem (2), for example, paragraph [0003] of Japanese Patent Laid-Open Publication No. 2009-90304 (Patent Literature 3) describes that “The paste for jointing before heating is a mere mixture of active metal powder and a metal powder having a composition as the balance, and has problems that alloying before heating does not proceed sufficiently so that the strength tend to be insufficient.” For the above problem (3), for example, the third paragraph in the introduction of “Denki Seikou” Vol. 74, No. 4, pages 227-232 (Non-Patent Literature 1) describes that “it is concerned that a reaction occurs between melting crucible and a molten titanium alloy to contaminate the titanium alloy powder from the material constituting the crucible.
[Citation List]
[Patent Literature]
[PTL 1] Japanese Patent Laid-Open Publication No. S59-220299
[PTL 2] Japanese Patent Laid-Open Publication No. S59-126739
[PTL 3] Japanese Patent. Laid-Open Publication No. 2009-90304
[PTL 4] Japanese Patent Laid-Open Publication No. H4-220198
[Non Patent Literature]
[NPL 1] “Denki Seikou” Vol. 74, No. 4, pages 227-232